The gating circuit used is a hybrid integrated analogue the switch drive and switch contacts. A negative 0.5 v bias switch (Fairchild SH3001) which uses metal-oxide-is applied to the trigger amplifier to prevent its firing on semiconductor transistors providing good isolation between noise produced in the transducer circuit. To prevent overdriving the switch ampmers, the trigger signal is limited to 5 v by 1 * 5 kQ series resstor.Each magnetic transducer signal is fed into a separate gating circuit (shaper and analogue switch). The output signal from the single photomultiplier tube is fed into, each gating circuit and is separated into four outputs and identified by the transducer trigger pulses for recording purposes.The instrument uses only one detector and one amplifier in place of four of the previous one. Spectral selection and dynamic range control can be achieved by using appropriate filters. Fillters of 1.) in. diameter will cover the aperture of the polarizing prism assembly and are readily available. Rapid spectral selection can be done by using the reference transducer pulse to trigger a stepper motor drive circuit. Since the light beam is continuously chopped, the problem of d.c. drift in the amplifiers is negligible. The aperture disk can be rotated at any desired speed up to a maximum of 400revmin-' which is fast enough even for measurements from an aircraft. Further details of the instrument will be published elsewhere.
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